An article titled "ISDN in the Office - HICOM," in a special issue of Telcom Report and Siemens Magazin COM discloses a modularly structured digital communication system that provides a uniform system for the communication of voice, text and data. The modular system structure is defined by independent function regions in the functional organization of the communication system. Internal interfaces are provided between these individual function regions. Critical function regions are a periphery, a switching matrix array and a central control.
In the periphery, connector modules provide for the interface adaptation between the communications system and equipment having a different communication type or a different signaling procedure. ISDN base terminals used for digital terminals wherein the signaling procedure is sequenced according to an ISDN protocol appear, for example, as subscriber-oriented equipment terminals. Further digital subscriber connector modules (SLMB--subscriber line module burst) provide for one-channel connection of digital voice terminals or switching terminals. Corresponding analog subscriber connector modules (SLMA--subscriber line module analog) are also utilized for the connection of analog voice terminal equipment. In a similar manner, line connector modules are also used as connection interface for analog and digital lines having the traffic modes of exchange traffic, tie trunk traffic as well as main system traffic and sub-system traffic. The connector modules each have a defined plurality of connection interface devices having line adapters as well as an assemblies processor control that is allocated to all of the connection interface equipment. One possible embodiment of such an assemblies processor control is disclosed in U.S. Pat. No. 4,694,452. The assemblies processor control distributes the voice signals or data signals from the connection interface equipment onto time channels of a PCM-structured link (highway) or, effects the coupling of the time channels of a second PCM-structured link to the connection interface equipment. In addition an HDLC interface equipment (high level data link control) is provided, signaling information in the HDLC protocol being forwarded via this equipment to a system controller. A microprocessor in the assemblies processor control executes the protocol control or the processor control and adapts the line signals to the interface messages of the system. The required programs are loaded from a background memory of the system into a memory administered by the microprocessor. The protocol according to ISO layers 1 and 2 is executed for digital connections, whereby the BORSCHT functions are realized for analog connections.
In the prior art communications system, a plurality of subscriber connector modules and/or line connector modules are functionally and structurally combined into a periphery module that is an interface module to the digital switching matrix network and to the system controller. The adaptation of the modularly structured communications system to a different plurality of connected terminal equipment or lines occurs by providing a corresponding plurality of subscriber connector modules or line connector modules per periphery module or by providing two or three periphery modules for an increasing plurality of subscriber or links.